This section provides background information related to the present disclosure which is not necessarily prior art. This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
Existing concepts for the design of helmets and armor include the use of impedance mismatch to reduce the amplitude of a stress wave. They also include the use of plasticity to absorb energy; it is also recognized that some visco-elastic materials are useful for blast mitigation.
The key concept of the present teachings is that if the stress waves from a blast or impact can be tuned to the critical damping frequency of a dissipative material, and the dissipative properties of the dissipative material are properly chosen, the energy can be dissipated in a very efficient fashion. Typically the energy of a blast or impact is contained in multiple frequencies, only some of which may be dissipated by passage through a given layer of a visco-elastic material.
The damaging features of blast and impact loads on a delicate target supported by a structure are shown to include both the overpressure and the impulse delivered to the support. The present teachings examine how layers of elastic, plastic, and visco-elastic materials may be assembled to mitigate these blast features. The impedance mismatch between two elastic layers is known to reduce the pressure, but dissipation is required to mitigate the transmitted impulse in light-weight armor. A novel design concept called blast tuning is introduced in which a multi-layered armor is used to tune a blast to specific frequencies that match the damping frequencies of visco-elastic layers. Moreover, the dimensionless material and geometrical parameters controlling the viscous dissipation of energy in blast-tuned armor are identified for a simplified one-dimensional system to provide insight into how the optimal design of armor might be based on these teachings. Finally, the performance of the blast-tuned design is compared to the performance of other potential designs, including elastic/plastic designs. It is shown that the blast-tuned armor design is more efficient in mitigating the damaging features of a blast or an impact.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
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